i6 ANTIENT METAPHYSICS. Book L 



But even fuppofing it to be true, that our bodies are moved by 

 ethers or fubtile fluids, Sir Ifaac fo far agrees with my dodtrine of 

 motion, that he thinks our bodies do not move themfelves. We 

 differ, however, as to the caufe of their motions; for, while I derive 

 them from mind, he maintains, as I have faid, that they are moved 

 by other bodies, fuch as ethers and fubtile fluids, operating upon them. 

 Now, this confirms me more and more in the obfervation I have made, 

 that Sir Ifaac had not fo much as the idea of body being moved by 

 mind, otherwife he could not have had the leaft doubt, that our 

 minds and bodies being fo intimately conncded, the motion of our 

 bodies was produced by our minds. I muft, therefore, hold, that 

 he believed that no other body is moved by mind, but that all the 

 motions of the univerfe are carried on by body moving itfelf or by 

 being moved by the impulfe of other bodies. 



Sir Ifaac maintains, that thefc ethers and fluids not only move our 

 bodies, but produce our fenfations*. This, I think, is the mod 

 unintelligible part of Sir Ifaac's philofophy of motion ; and it 

 proves to me, that Sir Ifaac did not fo much as know what fenfa- 

 tion is; for if he had known that it is produced by the a£lion of 

 external objcds upon our fenfes, and that it is the perception 

 by the mind of that adion, he never could have believed that 

 thefe ethers and fubtile fluids could have produced our fenfations: 

 For though, according to Sir Ifaac's dodrine, they produce the mo- 

 tion of our bodies, yet the adion by which they produce that mo- 

 tion is certainly not perceived by any of our fenfes, and therefore can 

 never give to the mind that perception which we C'nWfeJifatioft. 



Sir Ifaac, in order to complete his' fyfi:em of materialifm, fliould 



have 



* In this pafiage of Sir Ifaac's works, vphich is referred to in the preceding page, 

 he fays, that not only animal motions, but fenfations, are produced by ethers and 

 fubtile fluids. 



